This invention relates to an active magnetic bearing, i.e. a bearing in which magnets are actively controlled in order to affect the relative positioning of a rotor and a stator.
Active magnetic bearings are commercially available. Most of these bearings use only electromagnetic attraction forces to levitate and position rotor shafts. Such bearings are only able to pull on a ferromagnetic rotor, and this limits their maximum force capability. According to the present invention, pulling and pushing forces can be exerted on the rotor, thus giving the bearing a high force capability and reliability.
All of the energy and power used to support a rotor in a conventional magnetic bearing comes from the electrical energy supplied to the electromagnets. This requires a large power source and electronic switches. These components are very expensive and space-consuming. In contrast, an active magnetic bearing according to the present invention derives most of its energy and power from the kinetic energy of the rotor. The rotor receives this energy from a conventional prime mover. The overall effect is that the present invention makes it possible to reduce significantly the size and cost of the power supply and switching system.
Another deficiency of commercial active magnetic bearings is that they are highly non-linear. The force they provide varies significantly with changes in the rotor position and the field level in their saturable ferromagnetic rotors. This deficiency is overcome by the present invention since the rotor is made of nonmagnetic material which does not saturate. Therefore, the applied force does not change significantly with changes in the rotor position.
Another problem experienced with existing magnetic bearings is that, due to their inherent physical limitations, they cannot withstand momentary pulse loads. Bearings according to the invention can withstand very high pulse loads because they can withdraw large amounts of power from the rotor's kinetic energy. Other active magnetic bearings are able to produce about 100 psi of "magnetic pressure," while a bearing according to the invention can, for brief periods of time up to a few seconds, provide magnetic pressure exceeding 1000 psi.